Magnetoresistive effect elements such as a giant magnetoresistive (GMR) effect element and a tunnel magnetoresistive (TMR) effect element having a configuration in which a ferromagnetic layer as a magnetization fixed layer, a non-magnetic spacer layer, and a ferromagnetic layer as a magnetization free layer are stacked in this order are known. In recent years, such a magnetoresistive effect element has drawn attention as an element used in a magnetic sensor, a magnetic head, a magnetoresistive random access memory (MRAM), and the like.
The magnetization direction of the magnetization fixed layer in the magnetoresistive effect element is fixed such that the magnetization direction does not substantially change at the time of using the element. Thus, the magnetization direction of the magnetization fixed layer is not substantially changed by an external magnetic field (for example, a magnetic field of a measurement target in the magnetic sensor) and a spin torque (for example, a spin torque caused by spin injection magnetization reversal in the MRAM) that may be applied to the magnetization fixed layer at the time of using the element. However, when the fixing of the magnetization direction of the magnetization fixed layer is weakened due to any cause, and a deviation of the magnetization direction from a predetermined direction occurs, problems such as a decrease in magnetoresistive effect ratio (MR ratio) and a decrease in the symmetry of an output signal with respect to the external magnetic field are posed.
A ferromagnetic multilayer film called a synthesized anti-ferromagnetic structure (hereinafter, referred to as an “SAF structure”) is known as a technology for strongly fixing the magnetization direction of the magnetization fixed layer (refer to Patent Literatures 1 and 2 and Non-Patent Literatures 1 and 2). The SAF structure is composed of a first magnetization fixed layer formed of a ferromagnetic material, a second magnetization fixed layer formed of a ferromagnetic material, and a magnetic coupling layer that is formed of a non-magnetic metal and is interposed between the first magnetization fixed layer and the second magnetization fixed layer. The first magnetization fixed layer and the second magnetization fixed layer are antiferromagnetically coupled to each other by an exchange coupling magnetic field HEX via the magnetic coupling layer. Accordingly, magnetic flux occurring from the first magnetization fixed layer and magnetic flux occurring from the second magnetization fixed layer are distributed such that the magnetic fluxes as a whole forms a circulating path. The material and the film thickness of the magnetization coupling layer in the SAF structure are selected such that the exchange coupling magnetic field HEX is strengthened as far as possible. Accordingly, since the magnetization directions of the first magnetization fixed layer and the second magnetization fixed layer are not easily changed by the external magnetic field and the spin torque, the magnetization directions can be strongly fixed.